How to reinstall or upgrade my iMac macOS?
my imac 21.5 inch mid 2010 osx el capitan 10.11.6, ho to upgrade or reinstal
[Re-Titled by Moderator]
Welcome to the Apple Support Communities.
You can upgrade to macOS High Sierra. Download it from Safari here: How to get old versions of macOS - Apple Support. Backup first!
... or reinstal
Is there a reason you want to reinstall macOS? Are you having an issue?
Cheers,
Jack